The overall objective is to explore the control of myelination in the mammalian nervous system. Studies conducted to date have established that the behavior of the Schwann cell is controlled by the axon with which it is associated, the neuron instructing the cell whether or not to elaborate myelin. Proposed studies will examine grafts of optic nerves inserted in transsected peroneal nerves to determine if regenerated peripheral axons will stimulate oligodendrocytes to elaborate myelin. A positive result would suggest that there is a common signal for myelination throughout the nervous system. The fate of chronically denervated peripheral nerves will be further studied to determine the optimum time to harvest Schwann cells and the fate of these cells in the absence of axons. Schwann cells from denervated nerve stumps will be transplanted to the anterior region of the eye in an attempt to establish a viable colony of isolated Schwann cells. Their behavior in this locus and their response to neuronal factors will be tested. Finally, perineurial windows (surgically created openings in the side of the nerve) will be studied to determine the fine structural features of peripheral demyelination and remyelination. Results of these studies will bear heavily on our understanding of the interrelationship between the neuron, its axon and the myelinating cell.